[boost] Re: Interest in smart pointer with value semantics?

From: Dan W. (danw_at_[hidden])
Date: 2004-01-05 14:34:48

Thornsten, I agree with you 99.325%.

As a former fellow Eiffel-er, command <-> query separation is my religion.

If you were to look at my C++ code:

A) A function that has ANY side-effect whatsoever, inside or outside its 
class, unfailingly returns void.

B) A function that returns anything but void, not only is it unfailingly 
declared const, but you can bet your life-savings on it, it is as pure 
as pure gets --i.e.: "deep_const".

And constness propagation is my default, by discipline:

C) You'd never see me calling a non-const function through a chain of 
pointers that starts with, or contains, a const pointer anywhere, unless 
I do it through ignorance of the library class I'm using.

D) You'd never see a class-const function of mine taking non-const 
pointers or references.

E) Very rarely you'd see me mixing value and reference members, and 
treating the reference members in a shallow way, unless I have a reason 
for it, in which case you'd see big blocks of comments.

So, if C++ were to adopt the meaning of const correctness you propose, 
it would probably have little effect on my code. (Not so for a lot of 
other existing code).

Now, as I mentioned to you earlier, 4 years ago there was a heated 
polemic in an Eiffel forum about this exact same subject:  What IS an 
object?  What does ownership mean?  Should constness propagate?

And this I find interesting:

In Eiffel, the lack of constness propagation INDEED violates command - 
query separation!  Unlike a C++ const member function, a query function, 
in Eiffel, is *expected* to have no side-effects, yet it CAN have 
side-effects through chained references.  In this sense, C++ is the 
language that has the more self-consistent definition;  and Eiffel the 
language that's broken.  And remember that Eiffel has "deep_copy()".

So, you'd think that Eiffel has some *seriously* compelling reasons to 
adopt constness propagation, right?  Does it?  Nope.

I think that, as arbitrary as some of the features of C++ may seem, it 
just happens to be sitting on a sweet spot of sorts... something I've 
grudgingly come to accept... I'd love to have the compiler enforce some 
of my most beloved programming disciplines;  but I wouldn't be prepared 
to pay just any price for it; --and I do want to be able to touch the 
metal underneath, if you know what I mean;  that's why I left Eiffel behind.

Just my $0.02